Large amounts of metallic dust, powder or fines are created in different processes in metallurgic industry, among other things from disintegration and screening. Another area in which metallic fines are collected is in gas filters or wet scrubbers, for example. The handling and recovery of these fines are often difficult and costly problems. The pressure from both public authorities and customers to find new solutions is constantly increasing. The earlier solution of landfilling is no longer a feasible solution and is in many countries illegal. Existing techniques for conversion and recovery are costly.
From an economical and environmental point of view, recovery is often a preferred solution to the above-mentioned problem of taking care of the dust. However, recovery often means some kind of external processing, resulting in transportation to plants and processes lying beside the normal chain of processes.
It is very difficult to return dust or fines directly to a furnace because its tendency to burn. Furthermore, due to the low weight of dust and fines, they are easily carried away by the gas to be mixed with the exhaust from the furnace, thus lowering the yield and constituting an environmental hazard.
A known solution to these problems is pelletization or briquetting of the dust or fines for subsequent feeding to a furnace. However, this solution is accompanied with the problem of extra costs for a separate plant for pelletization and binding agent.
In the case the fines are intermixed in a sludge or slurry, such as when the fines are recovered from wet scrubbers, there is a problem of extra costs for a separate plant for drying and the waste material.
Processes for the recovery of metals are described in the patent documents EP-A1-0618419, U.S. Pat. No. 5,108,496, U.S. Pat. No. 6,001,148, and JP 8295956. However, all these documents relates to processes wherein the starting material comprises non-metallic material, such as oxides.